In the last several years, individual nanoelectromechanical resonators have been used to establish record sensitivities in force (Rugar, et al. Nature 2004, 430, 329-332), position (LaHaye et al., Science 2004, 304, 74-77), mass (Naik, et al., Nat. Nanotechnol. 2009, 4, 445-450; Jensen, et al., Nat. Nanotechnol. 2008, 9, 533-537), and gas concentration (Li et al., Nat. Nanotechnol. 2007, 2, 114-120). The miniscule size of nanoelectromechanical system (NEMS) or micoelectromechanical system (MEMS) sensors gives them unprecedented sensitivity to external perturbations, but this often comes at a cost. For example, both the power these devices can use and the magnitude of signal they can produce decrease at smaller sizes. Moreover for gas sensors, the interaction cross-section with particular analytes in a gas or liquid environment can rapidly decrease as the active mechanical element becomes smaller, whether due to increased analyte diffusion time, interaction with non-active sensor regions, or noisy, stochastic absorption/desorption of trace analyte levels (Arlett et al., Nat. Nanotechnol. 2007, 6, 203-15). In this limit of “needle in a haystack” detection, individual NEMS may have difficulty capturing even a single molecule of the analyte. Such challenges can make it difficult to exploit the full potential of individual NEMS sensors in the next generation of real-world microanalytical tools.
It is therefore desirable to scale up the interaction cross-section of NEMS sensors while still maintaining, or even enhancing, their extraordinary sensitivities and useful attributes. One approach to this task is simply to combine individual devices into arrays. For chemical sensors, different devices within the array can serve as detectors of different chemical compounds. Such arrays have previously been fabricated from microscale cantilever resonators (Zhang et al, Nat. Nanotechnol. 2006, 1, 214-220), microscale membrane resonators (Lee et al, Proc. IEEE Sensors Conf 2010, 2122-2126), nanoscale cantilevers (Li et al., Nano Lett. 2010, 10 3899-3903), nanoscale doubly clamped beam resonators (Sampathkumar et al., Nano Lett. 2011, 11 1014-1019), and nanowire resonators (Li et al., Nat. Nanotechnol. 2008, 3, 88-92).
Alternatively, one can use the collective response of multiple elements of the array to enhance the signal-to-noise ratio or other properties. For example, by engineering the mechanical coupling between individual resonators, one can produce a collective mode of oscillation that inherits the positive characteristics of individual resonators, such as high frequency and quality factor, but is able to handle more power (Li et al., Disk-array design for suppression of unwanted modes in micromechanical composite-array filters, Tech. Digest, 19th IEEE Int. Conf on MicroElectroMechanical Systems (MEMS'06), Istanbul, Turkey, Jan. 22-26, 2006). Such collective modes can then be further optimized to produce the desired overall response, for example, that of a bandpass filter (Li et al, An MSI micromechanical differential disk-array filter, Digest of Tech. Papers, 14th Int. Conf on Solid-State Sensors & Actuators (Transducers'07), Lyon, France, Jun. 11-14, 2007).
Despite these advances, presently available sensors are in many if not all cases still lacking in one or more factors such as, for example, ease of use, power handling, sensitivity and robustness.